1. Field of the Invention.
The present invention generally relates to protection systems and more particularly to an improved door burglar alarm system.
2. Description of the Prior Art.
Certain conventional burglar alarm systems for doors are quite complicated, bulky and expensive. Only a few are designed to be used in detecting surreptitious movement of a doorknob. Of these designed for that purpose, several require complicated and expensive electrical circuitry, including a plurality of switches, one or more for each direction of rotation of the doorknob. Certain others encumber the doorknob with clumsy hanging weights and the like. Still others provide plunger pins and other friction devices which are difficult and/or unsightly to install and may hinder rotation of the doorknob.
Accordingly, there remains a need for a simple, easily installed, inexpensive, attractive and highly effective means for detecting surreptitious rotation of doorknobs, which means should not in any way interfere with normal operation of the door and should encourage extensive use by homeowners, storekeepers, etc., particularly in view of the number of burglaries of both homes and businesses.